From 3aef00f466359e0f7ecc03a5aa71ebc5a318d1b9 Mon Sep 17 00:00:00 2001
From: myT <>
Date: Wed, 12 Feb 2025 03:25:43 +0100
Subject: [PATCH] fixed the blend equations to match the GL/D3D specs

---
 code/renderer/shaders/common/blend.hlsli      | 42 +++++++++----------
 code/renderer/shaders/crp/transp_resolve.hlsl |  2 +-
 2 files changed, 22 insertions(+), 22 deletions(-)

diff --git a/code/renderer/shaders/common/blend.hlsli b/code/renderer/shaders/common/blend.hlsli
index 298d4f5..df2366d 100644
--- a/code/renderer/shaders/common/blend.hlsli
+++ b/code/renderer/shaders/common/blend.hlsli
@@ -26,56 +26,56 @@ along with Challenge Quake 3. If not, see <https://www.gnu.org/licenses/>.
 #endif
 
 
-float4 BlendSource(float4 src, float4 dst, uint stateBits)
+float4 BlendFactorSource(float4 src, float4 dst, uint stateBits)
 {
 	if(stateBits == GLS_SRCBLEND_ZERO)
 		return float4(0.0, 0.0, 0.0, 0.0);
 	else if(stateBits == GLS_SRCBLEND_ONE)
-		return src;
+		return float4(1.0, 1.0, 1.0, 1.0);
 	else if(stateBits == GLS_SRCBLEND_DST_COLOR)
-		return src * dst;
+		return dst;
 	else if(stateBits == GLS_SRCBLEND_ONE_MINUS_DST_COLOR)
-		return src * (float4(1.0, 1.0, 1.0, 1.0) - dst);
+		return float4(1.0, 1.0, 1.0, 1.0) - dst;
 	else if(stateBits == GLS_SRCBLEND_SRC_ALPHA)
-		return src * float4(src.a, src.a, src.a, 1.0);
+		return src.aaaa;
 	else if(stateBits == GLS_SRCBLEND_ONE_MINUS_SRC_ALPHA)
-		return src * float4(1.0 - src.a, 1.0 - src.a, 1.0 - src.a, 1.0);
+		return (1.0 - src.a).xxxx;
 	else if(stateBits == GLS_SRCBLEND_DST_ALPHA)
-		return src * float4(dst.a, dst.a, dst.a, 1.0);
+		return dst.aaaa;
 	else if(stateBits == GLS_SRCBLEND_ONE_MINUS_DST_ALPHA)
-		return src * float4(1.0 - dst.a, 1.0 - dst.a, 1.0 - dst.a, 1.0);
+		return (1.0 - dst.a).xxxx;
 	else if(stateBits == GLS_SRCBLEND_ALPHA_SATURATE)
-		return src * float4(src.a, src.a, src.a, 1.0);
+		return float4(min(src.a, 1.0 - dst.a).xxx, 1.0);
 	else
-		return src;
+		return float4(1.0, 1.0, 1.0, 1.0); // 0 => replace mode
 }
 
-float4 BlendDest(float4 src, float4 dst, uint stateBits)
+float4 BlendFactorDest(float4 src, float4 dst, uint stateBits)
 {
 	if(stateBits == GLS_DSTBLEND_ZERO)
 		return float4(0.0, 0.0, 0.0, 0.0);
 	else if(stateBits == GLS_DSTBLEND_ONE)
-		return dst;
+		return float4(1.0, 1.0, 1.0, 1.0);
 	else if(stateBits == GLS_DSTBLEND_SRC_COLOR)
-		return dst * src;
+		return src;
 	else if(stateBits == GLS_DSTBLEND_ONE_MINUS_SRC_COLOR)
-		return dst * float4(1.0 - src.r, 1.0 - src.g, 1.0 - src.b, 1.0 - src.a);
+		return float4(1.0, 1.0, 1.0, 1.0) - src;
 	else if(stateBits == GLS_DSTBLEND_SRC_ALPHA)
-		return dst * float4(src.a, src.a, src.a, 1.0);
+		return src.aaaa;
 	else if(stateBits == GLS_DSTBLEND_ONE_MINUS_SRC_ALPHA)
-		return dst * float4(1.0 - src.a, 1.0 - src.a, 1.0 - src.a, 0.0);
+		return (1.0 - src.a).xxxx;
 	else if(stateBits == GLS_DSTBLEND_DST_ALPHA)
-		return dst * float4(dst.a, dst.a, dst.a, 1.0);
+		return dst.aaaa;
 	else if(stateBits == GLS_DSTBLEND_ONE_MINUS_DST_ALPHA)
-		return dst * float4(1.0 - dst.a, 1.0 - dst.a, 1.0 - dst.a, 1.0);
+		return (1.0 - dst.a).xxxx;
 	else
-		return float4(0.0, 0.0, 0.0, 0.0);
+		return float4(0.0, 0.0, 0.0, 0.0); // 0 => replace mode
 }
 
 float4 Blend(float4 src, float4 dst, uint stateBits)
 {
-	float4 srcOut = BlendSource(src, dst, stateBits & GLS_SRCBLEND_BITS);
-	float4 dstOut = BlendDest(src, dst, stateBits & GLS_DSTBLEND_BITS);
+	float4 srcOut = src * BlendFactorSource(src, dst, stateBits & GLS_SRCBLEND_BITS);
+	float4 dstOut = dst * BlendFactorDest(src, dst, stateBits & GLS_DSTBLEND_BITS);
 
 	return srcOut + dstOut;
 }
diff --git a/code/renderer/shaders/crp/transp_resolve.hlsl b/code/renderer/shaders/crp/transp_resolve.hlsl
index 3fc1aca..f316704 100644
--- a/code/renderer/shaders/crp/transp_resolve.hlsl
+++ b/code/renderer/shaders/crp/transp_resolve.hlsl
@@ -162,7 +162,7 @@ float3 BlendInScatteredLight(float4 srcColor, float3 dstColor, uint blendBits)
 	}
 
 	uint dstBlend = blendBits & GLS_DSTBLEND_BITS;
-	float3 dstContrib = BlendDest(srcColor, float4(dstColor, 1), dstBlend).rgb;
+	float3 dstContrib = dstColor * BlendFactorDest(srcColor, float4(dstColor, 1), dstBlend).rgb;
 	float3 result = srcContrib + dstContrib;
 
 	return result;